1. Field of the Invention
The present invention relates to a displacement control valve of a variable displacement compressor, which is suitable for use in an automobile air conditioning system and the like, and more specifically, to an improved mechanism of the displacement control valve which maintains a smooth operation. Moreover, the invention relates to compressors comprising such control valves.
2. Description of Related Art
Variable displacement compressors provided in a refrigerant circuits for automobile air conditioning systems, for example, the variable displacement compressor disclosed in Japanese Patent No. JP-A-2000-18172 are known. As depicted in FIG. 3, this variable displacement compressor 50 has a cylinder block 51 with a plurality of cylinder bores 51a, a front housing 52 provided on one end of cylinder block 51, and a rear housing 53 provided on the other end of cylinder block 51 via a valve plate 54. A drive shaft 56 is provided across a crank chamber 55 which is formed by cylinder block 51 and front housing 52. An inclined plate 57 is disposed around drive shaft 56. A rotor 58 is fixed on drive shaft 56, and inclined plate 57 is connected to rotor 58 via a joint portion 59.
One end of drive shaft 56 extends up to the outside of front housing 52 through the interior of a boss portion 52a which protrude from front housing 52. An electromagnetic clutch 70 is provided around boss portion 52a via a bearing 60. Electromagnetic clutch 70 comprises a rotor 71 provided around boss portion 52a, an electromagnet 72 contained in rotor 71, and a clutch plate 73 provided on an end surface of rotor 71. Clutch plate 73 is connected to one end of drive shaft 56 via a fastener 74, such as a bolt. A seal member 52b is interposed between drive shaft 56 and boss portion 52a, and the inside and the outside of the compressor are sealed from each other. The other end of drive shaft 56 is present in cylinder block 51, and the other end is supported by a supporting member 78. Bearings 75 and 77 are provided around drive shaft 56, and a bearing 76 is provided on an end surface of rotor 58.
A piston 62 is inserted slidably into each cylinder bore 51a. The radially outer portion of inclined plate 57 is received in a concave portion 62a which is formed on the inner end portion of piston 62. The radially outer portion of inclined plate 57 slidably engages a pair of shoes 63, so that the rotational movement of inclined plate 57 is transformed into the reciprocating movement of piston 62.
A suction chamber 65 and a discharge chamber 64 are defined in rear housing 53 separately from each other. Suction chamber 65 communicates with cylinder bore 51a via a suction port 81, which is provided on valve plate 54, and via a suction valve (not shown). Discharge chamber 64 can communicate with cylinder bore 51a via a discharge port 82, which is provided on valve plate 54, and via a discharge valve (not shown). Suction chamber 65 communicates with crank chamber 55 via an orifice 83, which is opened on valve plate 54, and via a refrigerant chamber 84, which is formed at a position on the end surface of drive shaft 56.
A displacement control valve 10 is provided in a concave portion which is formed on the rear wall of rear housing 53 of this variable displacement compressor 50. As depicted in FIG. 4, displacement control valve 10 is provided in a control mechanism equity 53a which is formed within the end portion of rear housing 53. Displacement control valve 10 has a valve casing 1 with a valve casing body 1a and a cap 1b provided on the end of the valve casing body 1a. A bellows 2 is disposed as a pressure sensing means in a pressure sensing chamber formed at an end portion in valve casing 1. Bellows 2 comprises a bellows body 2b, shaft members 2d which project from the respective inner ends of bellows body 2b and the tips of which are disposed separately from each other, an inner spring 2a disposed around shaft members 2d in bellows body 2b, and a support member 2c provided on and contiguous with the end of bellows body 2b. The inside of bellows body 2b is set substantially in a vacuum condition. A spring 3 is disposed around support member 2c to urge bellows body 2b toward an end surface of cap 1b via shaft members 2d. Bellows 2 functions as a pressure sensing means for detecting a pressure in suction chamber 65 (hereinafter, “a suction pressure”).
A rod passage 1c is provided in valve casing body 1a and extends through valve casing body 1a in the axial direction of displacement control valve 10. A pressure sensitive rod 4 is inserted into rod passage 1c within valve casing body 1a and supported by valve casing body 1a. One end of pressure sensitive rod 4 contacts the upper end of support member 2c of bellows 2, and the other end of pressure sensitive rod 4 contacts a valve body 5a which is formed as a large-diameter part on one end of a valve mechanism 5. Because bellows 2 is a pressure sensing means, and because pressure sensitive rod 4 is connected operatively to bellows 2, valve body 5a opens or closes communication paths 66, 1g, 1d, 1e, and 68 between discharge chamber 64 and crank chamber 55 in accordance with the expansion or contraction of bellows 2. A fixed core 7 with a rod guide passage 7a is disposed around valve mechanism 5. The lower end of core 7 contacts the upper end of valve casing body 1a. Core 7 slidably supports a valve shaft 5b of valve body 5a (hereinafter, “a solenoid rod”). Valve casing body 1a and a first end of fixed core 7 form a valve chamber 6. Specifically, one end portion of valve mechanism 5 is received in valve chamber 6.
Valve chamber 6 communicates with discharge chamber 64 via communication path 68, chamber 14, and communication path 1e. A plunger 9 is provided on a second end of fixed core 7. A tube 8 covers plunger 9 and a part of fixed core 7. A plunger chamber 11 is defined by fixed core 7 and tube 8. A communication path 13 communicates between plunger chamber 11 and suction chamber 65 via communication path 67, orifices 1f, and pressure sensing space 15. A solenoid 12 formed by an electromagnetic coil is disposed around tube 8. Solenoid 12 creates a magnetic field for applying an electromagnetic force on a gap between plunger 9 and fixed core 7 and applying the electromagnetic force to valve body 5a via solenoid rod 5b. 
In such a displacement control valve 10, the displacement is changed by adjusting the opening degree of the control path which connects the discharge chamber and the crank chamber.
In the above-described mechanism of displacement control valve 10, the gaps between rods 4 and 5b slidably inserted and rod passages 1c and 7a, respectively, are designed with close clearances to suppress refrigerant leakage. However, a shift may occur between the axes of rods 4 and 5b and the axes of rod passages 1c and 7a by a finishing error or an assembly error. In particular, as depicted in FIG. 5, in a case in which there is a shift in angle between the axes, the orientation of gaps between rods 4 and 5b and rod passages 1c and 7a are offset from each other by 180 degrees between the entrance portions and the exit portions of rod passages 1c and 7a. In other words, the orientation having a maximum gap at the entrance portion becomes a orientation having a minimum gap at the exit portion. On the other hand, because rod passages 1c and 7a are provided in respective partition walls, both end parts partitioned by each partition wall experience a pressure difference, and a portion of refrigerant flows into the above-described clearance from the increased pressure side to the reduced pressure side. At that time, fine foreign materials contained in the refrigerant may enter into this clearance. If there is a shift between axes, the foreign materials having entered from the maximum gap direction into the clearance may not be discharged from the gap between the rod and the rod passage, depending on the size of the foreign materials. Further, the foreign materials may damage the movement of the rod by wedging within the clearance(s), and it may degrade operation of the control valve and may cause poor control on compressor displacement.
Such a situation may be better understood with reference to FIG. 5. With respect to solenoid rod 5b, a discharge pressure is operating in space 6, and on the other hand, a suction pressure is operating in plunger chamber 11 because chamber 11 communicates with suction chamber 65. Therefore, refrigerant flows from space 6 to plunger chamber 11 through the gap between solenoid rod 5b and rod passage 7a, and at that time, fine foreign materials may enter into the gap. As depicted in FIG. 5, in a case where the axis of solenoid rod 5b inclines relative to the axis of rod passage 7a, foreign materials having entered from the larger gap may be brought into a deep portion by the refrigerant flow. When solenoid rod 5b is inclined, the gap may decrease in size gradually, and at last, the foreign materials having entered may be pressed between solenoid rod 5b and rod passage 7a, thereby damaging the movement of solenoid rod 5b. In addition, with respect to the pressure sensitive rod 4 side, because a pressure in the crank chamber and a suction pressure operate on the upper and lower sides thereof, foreign materials may be drawn into the gap by the pressure difference. Consequently, foreign materials having a certain size may not be discharged and may be pressed within rod passage 1c, thereby damaging the movement of pressure sensitive rod 4.